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X3 E83 (2004 - 2010)
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  #1  
Old 08-14-2014, 01:56 PM
gnagflow gnagflow is offline
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Engine stumble / hiccup at throttle tip-in

Hi,

my first post, so please bear with me...

I noticed a slight engine stumble when accelerating from a stop. When tipping in the accelerator the RPMs momentarily drop and then the engine revs normally. It's most noticeable when the engine is under load (AC on, in D) and almost gone when the car is in P or N.

It's very easily reproducible by putting the car in D, turning on the AC and then very slightly pushing the accelerator (with left foot on the brake). Short RPM drop, followed by normal revving. Interestingly, the stumble becomes more noticeable the longer I wait between tip-ins. For example, if I tip-in, get the stumble, then tip-in right away, there's no second stumble. If I tip-in, get the stumble, then wait for a few seconds before the second tip-in, I get a second stumble. The second stumble seems to get worse (to a point) the longer it sits in idle.

Idle itself is pretty solid with the occasional surge (could be AC engaging). Also there is a slight RPM dance when you put it from P/N to D/R. Sometimes there's a slight RPM hunting oscillation when coming to a stop, but it settles after a few seconds.

On a cold start in the morning the idle RPM seems to fluctuate a little before it settles in. You can pretty much tell when it goes from open loop to measured mode.

Other than that the car runs fine. It has about 55k miles on it. I hooked up INPA and could not find any abnormal readings so far.

So far I have done the following:
- Updated ECU and transmission software (made huge difference in shift behavior)
- Cleaned throttle body (it's a N52 with valvetronic, still cleaned it)
- New air filter
- Checked for air leaks, so far found none
- Cleaned the MAF
- Replaced VANOS solenoids around 15k miles ago

Is there a way to check the MAF for tip-in behavior? INPA shows reasonable air flow values (~16-18 kg/h) but maybe on tip-in the MAF does not behave well?

Does anybody else experience this, or can anyone else reproduce the problem? What am I missing?

Thanks,
Wolfgang
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  #2  
Old 08-14-2014, 03:23 PM
iamjamen iamjamen is offline
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No codes thrown, CEL?
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  #3  
Old 08-14-2014, 05:08 PM
gnagflow gnagflow is offline
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Quote:
Originally Posted by iamjamen View Post
No codes thrown, CEL?
No, did not get any error codes and no CEL.

However, I noticed something else: In INPA, when I selectively clear the adaption for VANOS it seems to be better for a short while. Not sure, though.

Does VANOS play a big role in tip-in behavior?

Wolfgang
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  #4  
Old 08-14-2014, 05:20 PM
joylove joylove is offline
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Do not clear the adaptations when the engine is running.

How do the O2 sensors look? some report this issue can improve with new sensors.
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  #5  
Old 08-14-2014, 05:29 PM
gnagflow gnagflow is offline
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Quote:
Originally Posted by joylove View Post
Do not clear the adaptations when the engine is running.

How do the O2 sensors look? some report this issue can improve with new sensors.
I have looked at the O2 sensor data a while back and they all were in the green range. Don't recall exact values anymore, though. Will try to take a screenshot later and post.

Then again, sometimes it's hard to tell in INPA whether or not a value is within specs. Would be interesting what values other people are seeing.
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  #6  
Old 08-14-2014, 11:32 PM
joylove joylove is offline
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They get sluggish when they are old. Try to plot a graph and blip the throttle to see if they aren't asymmetrical. Under static conditions they should be merrily toggling between rich and lean indicating a closed loop fueling. .
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  #7  
Old 08-15-2014, 12:32 AM
gnagflow gnagflow is offline
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Here's a screenshot I took with the engine idling. The values for the two sensors seem to move in tandem when applying the throttle.
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  #8  
Old 08-15-2014, 10:03 AM
gnagflow gnagflow is offline
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Quote:
Originally Posted by joylove View Post
They get sluggish when they are old. Try to plot a graph and blip the throttle to see if they aren't asymmetrical. Under static conditions they should be merrily toggling between rich and lean indicating a closed loop fueling. .
That's a great suggestion. Unfortunately, I don't have the tools it takes to capture the data and plot a graph. In INPA I get a couple screens that show me values, but again, all of them don't really mean a lot by themselves. They do seem to settle into similar values though at idle. I attached a screenshot in another post. All the values are in the "green" range which suggests that there is no problem... right?
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  #9  
Old 09-03-2014, 12:20 PM
gnagflow gnagflow is offline
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Wanted to follow up with a couple more things.

I have been to a indie BMW shop and while they have been able to reproduce the problem they have not seen this before. They said they will ask in a BMW internal forum and see if any other shops have run across this before.

It seems that the temperature measures by the air intake temp sensor is always higher than the ambient temperature sensor. This is according to INPA looking at the MWB3 data. For example, at a cold start in the morning the ambient temperature may be 27C and the air intake sensor reads 32C. The difference is typically between 3 and 6C.

When idling the ignition timing is around 0. When slightly tipping in the throttle to reproduce the problem, the engine stumbles and the ignition timing momentarily retards to around -16 before getting back to around 0. It seems that even though the throttle is only very slightly applied, the ignition timing retards quite a bit.

Could it be that because of the high intake air temperature reading the air mass is calculated wrong? With the temperature reading to high, the calculated mass based on the MAF cooling would be too high which means that the ECU could think there's more air rushing in than there actually is causing the excess retard of the ignition timing.

Has anybody else seen the intake air temp read to high and diverge much from the ambient temperature reading? This is happening at cold start, so engine heat can not be a factor at this time.

Please report your experience and readings if you have any. Would be interesting to see what others are seeing.

Thanks,
Wolfgang
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  #10  
Old 09-03-2014, 01:07 PM
joylove joylove is offline
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A fixed offset from the ABS temperature should be compensatable in the software. Do the two temperatures maintain the 3-6C offset for all actual temperatures?
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  #11  
Old 09-03-2014, 02:25 PM
gnagflow gnagflow is offline
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Quote:
Originally Posted by joylove View Post
A fixed offset from the ABS temperature should be compensatable in the software. Do the two temperatures maintain the 3-6C offset for all actual temperatures?
They do initially. However, after the engine warmed up they can diverge much more, for example in stop-n-go traffic or after parking for a while. This is likely due to the engine radiating heat into the intake pipe, though. I have seen 60C+ after a stop while outside temp was 30C.

The interesting thing is that it does take some time, even when driving at higher speeds, until the intake <-> ambient temps get back together. You would expect that should happen pretty quickly as a lot of colder outside air is rushing in.

Wolfgang
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  #12  
Old 09-03-2014, 02:37 PM
joylove joylove is offline
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Actually the speed of the car should not affect the measured temperature. An object cannot experience "Wind chill" because there is no moisture evaporating from it (unlike human skin). The change in measured temperature comes from cold air next to the hot wire/resistor. So long as the air is continuously moving at the sensor surface then the cooling effect is the same. Only if you have 1mm of stationary air it becomes an insulator, and this is why the temperature rises slightly when stationary.


For your issue, the temp sensor offset and slope should all be learnable items by the software. Do you have any sporadic jumps in the measured temperature value e.g. to -40C (open circuit)?

Last edited by joylove; 09-03-2014 at 06:09 PM.
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  #13  
Old 09-03-2014, 02:55 PM
gnagflow gnagflow is offline
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Yes, there is no wind-chill, so as soon as the engine is running the intake air temperature should pretty quickly converge to the ambient temperature. I can see some warming of the air while it's traveling throughout the intake until it hits the sensor, but that should be marginal. So seeing 50-ishC while driving at 60mph while outside temp is 30C might indicate a problem.

I have not seen any jumps, the readings are pretty solid.

Also, I sprayed the sensor with MAF cleaner and it did drop significantly. However, this does not tell anything about the calibration of the sensor, just that it kinda works.

As for the adaptation, I would expect that the value displayed already is the corrected value.

I will try to get my hands on another MAF (which contains the IAT sensor) and see if it behaves the same.

Wolfgang
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  #14  
Old 10-09-2014, 10:32 AM
huwge23 huwge23 is offline
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Any update on this? I have noticed the same thing with my initial acceleration.
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  #15  
Old 10-09-2014, 04:55 PM
gnagflow gnagflow is offline
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Hi,

there's a small update and possibly a fix, but the jury is still out on this one.

I have noticed, looking at INPA, that the inlet VANOS solenoid was a little "jumpy", while the outlet solenoid was more stable, i.e. while the engine was idling, the inlet VANOS nominal value was unchanging, while the actual value was "dancing" around the nominal value a couple degrees up and down. The outlet VANOS was more stable. My conclusion was that the inlet solenoid may be a little "loose", maybe on its way out.

As the throttle is strongly linked to the inlet valve behavior, I decided to switch them around and after the switch the inlet VANOS actual value was not "dancing" anymore but solidly traced the nominal value. At the same time, the throttle response improved and did not show the stumble-stutter behavior anymore, at least most of the time.

After that, I installed a NEW inlet solenoid and put the more stable solenoid back on the outlet side. This did not make a huge difference, apparently the outlet valve behavior does not have as strong an impact on throttle behavior as the inlet one. So far, it's been OK, but not great. Maybe, it's just because I am now so tuned in to that problem that I still seem to notice a problem once in a while. Another person might not notice anything.

As I just did this a couple days ago, I don't want to declare victory just yet. There's also various changes in behavior after clearing adaptations of various settings. Still playing around with this.

Hope this helps,
Wolfgang
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  #16  
Old 10-09-2014, 05:44 PM
huwge23 huwge23 is offline
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No that definitely helps. I am very familiar with more common issues when fixing vehicles but nothing as in depth as you are speaking about. I know my cars well though and noticed this hesitation right away when I first drove the car. My wife doesn't really seem to notice and it is her car. I just want to keep an eye on it just in case it gets worse.

I would like to know if what you have done seems to help..even a little.
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  #17  
Old 10-09-2014, 05:52 PM
gnagflow gnagflow is offline
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I will post an update once I have more conclusive results.
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  #18  
Old 11-27-2014, 11:46 AM
gnagflow gnagflow is offline
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Hi, as promised, here is a quick update.

It's been a few months since I changed the intake solenoid. As mentioned before, there was an overall improvement in the tip-in response, but there was still the occasional hiccup, even though not as pronounced as before. Recently, my commute changed from 8 miles one way to 32 miles one way, mostly freeway. As some people in this forum mentioned that short commutes may contribute to engine problems I was hopeful that the longer commute might help to get rid of the stumbles and hiccups. No such luck...

I started to live with the issue, however, there was still one thing that bothered me. One of the codes that INPA reported was "EBox Fan Blower", which didn't seem that critical at the time as it neither caused an engine light, nor did the engine box temperature exceed the safe limit. Still, it might just be a blown fuse and a quick fix, so I went to check the fuses.

Fuses 27, 29 and 30 are marked as "engine control" and fuse 43 as "OBD". Removing and checking those showed that all of them were OK and the right value, so no luck there. Not surprisingly, the Instrument cluster was reset and I had to re-enter the time.

Now, the interesting thing is that the next day the car was completely transformed. The hiccup was pretty much gone (except for a stumble just after cold start) and the transmission shifts felt smoother. I should note that the transmission shifts improved dramatically after the software update a few months ago, but now they feel smoother still. There seems to be more low-end torque as well and there are fewer downshifts when slightly accelerating while cruising. Also, when flooring the car, it feels faster and power delivery is more even throughout the rev-band and shifts. Tip-in response is much better, too, it now feels as if the car really wants to accelerate when you press the accelerator, before it felt as if it was contemplating for a while whether or not to respond, and once it did, it was typically pretty abrupt...

It seems that power-cycling the ECU by pulling the fuses fixed the hiccup. One thing to note is that I did try to reset the ECU before by disconnecting the battery for a while. This had the same effect on the instrument cluster (i.e. had to re-enter the time) but it had no effect on the engine hiccups. This was, however, before the intake solenoid was replaced. This could mean that either the solenoid swap helped or that the battery disconnect does not have the same effect as pulling the fuses.

To summarize:
Initially the car had rough shifts, poor engine performance and tip-in hesitation
After updating the software, shifts and performance improved, still annoying hiccups at tip-in
After replacing the intake solenoid, slight improvement in tip-in, less pronounced hiccups
After power-cycling the ECU by pulling/replacing the engine control fuses, virtually no more hiccups and smoother shifting

I should also mention:
Cleaning the MAF and throttle body plate had no effect
Replacing the air filter had no effect
Replacing the battery with a higher rated model had no effect
Adding fuel injector cleaner had no effect

Some have reported that resetting the transmission or the ECU resulted in only temporary improvements and that things go back to "normal" after a re-learning phase. Well, I hope that's not the case here, but it's only been a couple days. Fingers crossed.

Wolfgang

Last edited by gnagflow; 11-29-2014 at 01:51 PM. Reason: Fixed commute distance.
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  #19  
Old 12-03-2014, 03:36 PM
huwge23 huwge23 is offline
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Awesome I will definitely try pulling the fuses. I will see if this changes anything and as you stated the new intake solenoid seemed to help as well.

As for updating the ECU and transmission software how would I do that? Is that similar to setting or disabling features set by the dealer?
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  #20  
Old 12-03-2014, 04:06 PM
gnagflow gnagflow is offline
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Hi,

hopefully it's going to work for you. As for the software update, you will need to go to a BMW dealership or a BMW certified shop that has the tools to flash the new software. Unfortunately, they will likely charge you around $150-$200 for doing that and it can take a few hours to finish until all the modules are updated. Some people have done this themselves, so it is definitely possible to DIY, but there is a risk of "bricking" the car when you do this and then you'd have to have it towed to the dealership anyways. Not worth the risk IMHO.

Please keep us posted on your experience with the fuse pulls!

Wolfgang
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  #21  
Old 12-04-2014, 05:30 AM
huwge23 huwge23 is offline
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I can see your point as I believe the software to do it at home is in that range of cost.

I will certainly keep you updated on the fuse pull and will likely try it tonight as I have to work on another vehicle anyway. Thank you for the info.
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  #22  
Old 12-19-2014, 07:42 AM
huwge23 huwge23 is offline
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I did try pulling the fuses as mentioned and this had no affect. I will try swapping the intake and exhaust solenoids to see if this has an affect on the hiccup. I would hate to buy a new solenoid and have that not be the issue.

It does make a lot of sense pointing in that direction though since you mentioned it plays a large part in throttle response.
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